On Thu, Oct 16, 2003 at 10:07:18PM -0400, Albert Cahalan wrote:> Tie directory readers to a task_struct (or to> some of the PID tracking structs), so that> a directory reader is on a list. When a task> exits, move the list of directory readers on> to a neighboring task.> That is O(1) on task exit, and generally O(n)> for the whole /proc or /proc/42/task read.> It's O(1) per step of the read, excepting> where multiple directory readers wind up at> the same location.> Another benefit is that it is reliable as> long as tasks don't move around on the lists.> Each task will appear at most once, and will> appear exactly once if it doesn't start or> exit during the directory scan.

Several other things have been tried.(a) something mingo wrote I forgot the nature of(b) a thing manfred wrote that recovers positions in hashtable collision chains by sorting them, with O(chain length) insertion(c) a thing I wrote that turns the tasklist and pid_chains into rbtrees and uses the last-seen pid to seek in O(lg(n)) time, and uses a routine to seek and fill buffers as a drop-in replacement for get_tgid_list()/get_tid_list().

I have a current implementation of (c), as well as a patch torestore 2.4 semantics to proc_pid_statm() in O(1) time.